Some scientists said the study was too small to be the final word, but it was one of the best done so far and came after three very large studies produced disappointing results using the same nutrients to try to prevent heart disease.
"We'd love to have something that is simple and reproducible and cheap and effective that would reduce the amount of dementia," but proof that vitamin supplements can do this is still lacking, said Bill Thies, scientific director of the Alzheimer's Association, which had no role in the study.
The findings were published in a recent issue of the New England Journal of Medicine.
Folate and B vitamins lower homocysteine, a blood substance that can make arteries stiffen and clog. Many studies have observed that people with higher levels of homocysteine also have a greater risk of heart disease, Alzheimer's and other forms of dementia.
But whether lowering homocysteine can prevent these problems is unknown. In two studies of people at high risk of dementia, vitamin pills did not help, but these experiments lasted less than four months.
